1. Field of the Invention
The invention relates to a system for displaying images and methods of fabricating the same and, more particularly, to a system for displaying images including active matrix organic electroluminescent devices and methods of fabricating the same.
2. Description of the Related Art
Please referring to FIG. 1, it is a schematic drawing showing a conventional pixel structure of an active matrix organic electroluminescent device (AM-OLED). The pixel structure 100 of an AM-OLED is electrically connected to a scan line 102 and a data line 104. The pixel structure 100 of the AM-OLED comprises a switching thin film transistor 110, a driving thin film transistor 120, a storage capacitor 130 and an organic light emitting diode 140. The gray level of the pixel structure 100 is determined by a data signal input from the data-line 104. When the switching thin film transistor 110 is turned on by a scanning signal input from the scan line 102, the capacitor 130 is charged to store the data signal. When the switching thin film transistor 110 is turned off, the driving thin film transistor 120 is controlled by the data signal stored in the capacitor 130 and a driving current corresponding to the data signal (gray level) is provided to the light emitting diode 140 through the driving thin film transistor 120. Specifically, the driving thin film transistor 120 is electrically connected to a power source Vdd. The current from the power source Vdd is adjusted by the driving thin film transistor 120 and the adjusted current (driving current) is provided to the light emitting diode 140 frame by frame.
Please continue to refer to FIG. 1, the switching thin film transistor 110 and the driving thin film transistor 120 can be, for example, an amorphous-silicon thin film transistor or a poly-silicon thin film transistor. Compared with the amorphous-silicon thin film transistor, the poly-silicon thin film transistor has the advantages of low power consumption and high electron mobility. Although the option of the substrate is constrained by the temperature for fabricating the poly-silicon thin film transistor earlier, the poly-silicon thin film transistor has become the mainstream of the active device according to the development of the low temperature poly-silicon technology.
The top gate thin film transistor has the advantages of large process window, simple fabrication process and small size. Therefore, top gate thin film transistors are broadly used in the pixel structures and the peripheral circuit of the conventional active matrix organic electroluminescent devices. The characteristic of top gate thin film transistors, however, are sensitive to the cleaning process before date insulator deposition, resulting in undesirable clean mura defects in the active matrix OLED devices.
Besides, for the bottom emission AM-OLED device, when the top gate thin film transistors serving as the switching thin film transistor expose to sunlight, current leakage occurs in the channel region even if the switching thin film transistor is turned off. The data signal stored in the storage capacitor would deteriorate and therefore affect the stability of the OLED display. Furthermore, the storage capacitor and the power line occupy the pixel area and this would reduce the aperture ratio of the pixel structure.
Therefore, it is necessary to develop a novel active matrix organic electroluminescent device to solve the aforementioned problems.